Wood-preservative treatment.



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WOOD-PRESERVATIVE TREATMENT.

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No Drawing.

To all whom it may concern:

Be it known that I, J UDsoN an]: Cnw, a,

subject of the King-of Great Britain, and resident of the city ofMontreal, in the Province of Quebec and Dominion of Canada, haveinvented certain new and useful Improvements in NVood-PreservativeTreatment, ofwhich the following is a full, clear, and exactdescription.

This invention relates to the treatment of wood products such as ties,timbers or the like, in order to preserve them from the effects ofmoisture, fungi or other destructive agents, thereby introducing newqualities of resistance to both decay and mechanical wear.

It is well known that timbers or Wood blocks for pavements, when fullyimpregnated with oily materials, such as creosote oil, are not madewaterproof thereby. This has been proved by the fact that drybloeks,when fully impregnated with oil, would expand after being laid in theground to such an extent as to destroy a laid pavement. This is due tothe fact that moisture can be absorbed by the cell Walls of a woodstructure, even though they are impregnated with and surrounded by oil.It has been shown and is generally recognized that the normal conditionsof cell wall saturation in oil impregnated timbers is one wherein thelignocellulose material contains approximately 20% moisture. This iscalled the normal point of saturation.

It is also known by extensive tests for determining the strength oftimbers at various points of saturation that an absolutely dry specimenof timber will show approximately twice the mechanical strength oftimbers carrying the normal amount of water saturation. It is also awell established fact that moisture is requisite for the decay anddestruction of timbers by means of ferment or fungi, and the dry timberswill last indefinitely. If it is possible, therefore, to maintain woodin an absolutely dry condition, the maximum strength and resistance towear can be maintained.

The object of my invention is to reduce the wood products first to abone dry condition, and then to impregnate and cover the surface of thewood in such a manner that moisture cannot again enter the wood and beabsorbed by the cell walls thereof.

The method of carry g t my pr cess is Specification of Letters Patent,

Application filed. August 11, 1916.

Patented (lot. 29, 1918.

Serial No. 114,449.

as follows :-The specimen is first immersed ina solution of hot coal tarpitch or tar and is left submerged therein until the air and moisture,which is contained in all green or air CllledllllllbBI'S, has beendriven off. To .accomphshthis, the pitch or tar solution must be heatedto a temperature of 212 Fahrenheit, or higher, depending upon the rateat which the moisture is to be expelled. Dry wood will commence to charwhen heated to atemperature above 250 F but this cha rring will not takeplace when moist timbers are being heated, and the steam is pass ingconstantly from the outside surface to the specimen. It is only afterthe moisture is practically all driven out from the speci men thatchar-ring of the, surface will take place, and when this action isnoticed, this portion of the treatment may be terminated.

The specimen is then taken out of the tank or other receptacle. andallowed to cool until.

the average temperature is below the boiling point of water, when apractical vacuum will exist in the cells within the specimen. If, now,the entire specimen is again heated until the pitch on the surface is ina liquid condition, it will be drawn into the cells of the wood tofill-this vacuum. This second heating step can be carried out byimmersing it for a second time in the molten coal tar pitch at a propertemperature, or by heating it in a chamber in which the ten'iperature iscontrolled by means of air or steam, and in which pressure may also beapplied. Owing to its viscosity, a deep impregnation will not beobtained when using a material such as coal tar pitch, but this is notnecessary nor desirable, as long as the impregnation is sufficientlydeep to thoroughly plug and waterproof the exterior portions of thematerial, then, the inner part of the wood will be preserved from bothmoisture and decay. It is desirable to obtain not only a limited depthof impregnation but also a surface coating, which will prevent theexposure of the cell walls to atmospheric influences. The resultantprocluct of my invention is a timber in which the heart of the specimenis dry, sterile and under partial vacuum. The surface comprises a layerof impregnated wood covered with a coating which prevents access ofmoisture. If the impregnating pitch used is of a soft and stickyconsistency when cold, an. additional surface coating may be given bydipping the specimen into a tank of very hard pitch in a hot moltencondition.

The first part of my process is carried out in open tanks so arrangedthat the specimens, either singly or in bundles, can be immersed andheld below the surface. The second part of the process consists eitherin the application of heat and pressure within a closed cylinder tank inorder to forcethe soft pitch into the cells of the wood, or it mayconsist of successive heating and cool ing operations by dipping thespecimen intermittently into the hot material, in which case the hotpitch will be forced into the cells by means of atmospheric pressure.The wood product thus treated will be harder and stronger than woodtreated by the usual processes on account of its bone dry condition.

Having thus described my invention, what I claim is y 1. A process oftreating wood, which consists in heating the wood in solution of coaltar pitch at practically a charring temperature, expelling the water ofsaturation from the fibers 0f the wood, impregnating the outer portionof the wood with the material in which it is immersed, coating thesurface with a harder pitch at higher temperatures and leavingsufficient coating on the surface to keep the surface fibers of the woodfrom contact with moisture.

2. A process of treating wood, which consists in heating the wood to asterilizing temperature, removing the water of saturation from the cellwalls of the fibers, impregnating the outer portion of the wood with asolution of coal tar pitch, and coating the surface of the wood with aharder pitch at higher temperatures to prevent the fibers from againabsorbing the water of saturation.

3. A process of treating wood, which consists in heating the wood at asterilizing temperature until the water of saturation is removed,impregnating the outer portion with a solution of coal tar pitch whichis fluid at temperatures below 212 Fahrenheit, and finally dipping intemperatures above 212 Fahrenheit.

In Witness whereof, I have hereunto set my hand, in the presence of twowitnesses.

J UDSON A. DE OEW.

Witnesses:

S. R. W. ALLEN, G. M. MORELAND.

u Copies of this patent may be obtained for five cents each, byaddressing the Commissioner of IPatents,

Washington, I). G.

